With the high number of auto larceny incidents, the search has continued for a reliable and effective alarm system for use with automobiles. There are numerous American patents in this area, as exemplified by Raschke, U.S. Pat. No. 3,579,233; Teich, U.S. Pat. No. 3,956,732; Carlson, U.S. Pat. No. 3,852,614 and Rubin, U.S. Pat. No. 3,422,398. The devices described in the above patents all disclose some means to protect an automobile against various unauthorized invasions. Of particular interest is Fischer, U.S. Pat. No. 3,794,967, wherein the invention detects transient changes in the automobile electrical system. A transistor latching circuit operates a horn in response to such transients. Fischer's teaching thereby points toward an improved means for activating an automobile intrusion alarm.
The prior art contains numerous problems, however in providing an effective alarm. Once activated, many systems, including Fischer, sound an alarm until manually disengaged, or the auto battery wears down, both eventualities of considerable inconvenience. Those devices that do automatically disengage often do not rearm themselves, or if they do, their trigger means may be circumvented if an unauthorized person remained in the auto. The devices often rely on complex circuitry that places no emphasis or reliance on state-of-the-art components. The reverse is also true, with some devices containing expensive components that are just as inefficient from a design point of view as the more remedial circuits.
In addition, it must be remembered that automobile alarm devices are rarely if ever factory installed by the automobile manufacturers. Rather, the devices must be installed after the auto is sold. Many devices overlook this particular aspect and are consequently difficult to install.
Therefore, a need exists for a conveniently installed, effective automobile alarm device that is highly efficient and therefore inexpensive.